Continued investigations on the mechanisms of regulation of HMG-CoA reductase, acetyl-CoA carboxylase and cholesterol 7 alpha-hydroxylase activities are proposed. In these studies we shall attempt to complete our studies to determine whether specific nutritional and hormonal factors regulate HMG-CoA reductase activity in vivo by modification of pre-existing enzyme or by a change in the rate of synthesis of the enzyme. If any condition is found under which short-term regulation occurs, we will proceed to isolate and study the factors that effect such a regulation. We will also initiate experiments that are directed towards an understanding of the mechanism by which various nutritional and hormonal factors regulate the synthesis of HMG-CoA reductase. Studies on the regulation of acetyl-CoA carboxylase will concentrate on the purification of a protein from rat liver that inactivates this enzyme and on the establishment of the mechanism by which this protein acts. Studies may also be initiated on the isolation of mRNA for acetyl-CoA carboxylase and a determination of the mechanisms by which the quantity of this mRNA is regulated in rat liver. Studies on cholesterol 7 alpha-hydroxylase will be directed towards attempts to purify this enzyme to homogeneity. If successful, we will prepare an antibody to this protein.